A games of .hack attempt to simulate the MMORPG entitled The World within a game while forgoing actually existence on the net; this is achieved by an emulation of the ALTIMIT OS on which the RPG client purportedly diarrhea, across which professional people could prevent fabricated e-electronic mail, newspaper article, & message boards, additionally to the game itself. A games come particularly unique for their ability to part save information between every release via "data flags", upgrading it for both release to produce it playable & carrying above save information for such (though of these might commence any title in the series from either scratch.)

Involved by having both game is an additional DVD containing an OVA from .hack//Liminality.

As an added bonus, .hack//GIFT, a one-off OAV that mocks the entire .hack franchise, is viewable for free on the Liminality disc that comes with the North American release of .hack//QUARANTINE; in Japan, players had to retrieve the fourth and final data flag in .QUARANTINE to view GIFT.

Series Titles
.hack//INFECTION (Japanese: .hack//感染拡大 Vol.1 [Infection Expansion – Vol.1]) .hack//MUTATION (Japanese: .hack//悪性変異 Vol.2 [Malignant Mutation – Vol.2]) .hack//OUTBREAK (Japanese: .hack//侵食汚染 Vol.3 [Erosion Pollution – Vol.3]) .hack//QUARANTINE (Japanese: .hack//絶対包囲 Vol.4 [Absolute Encirclement – Vol.4])